As labor costs rise, it becomes of increasing importance to reduce the time required to assemble a telephone instrument. One way of reducing assembly time is to eliminate the use of fasteners both to assemble components to a housing member and to assemble housing members together. As shown in Gruger et al U.S. Pat. Nos. 3,617,658 and Schwank et al 3,657,487 this may be accomplished by the use of flexible latch elements that are deflected from their normal position in the process of assembly and then return to their normal position to perform their latch function when assembly is complete.
The problem with this arrangement is that in order for a telephone instrument to quality under the registration rules of the Federal Communications Commission, it must withstand six random drops from 30 inches onto a concrete floor. This drop test is intended to simulate the shock a telephone instrument may encounter during loading, shipping, and unloading as it moves from the manufacturer to a distributor, from the distributor to a supplier, and from the supplier to the premises of a user. It has been found that the impact from such a drop can cause flexible latch elements to deflect and release the housing members and/or components that they are intended to secure. While the interest of the Federal Communications Commission is avoiding damage to the telephone instrument that will cause harm to the telephone network, from the manufacturer's standpoint it is undesirable to have the telephone instrument come apart even if no harm to the network results.
Another matter of concern with respect to the structural arrangement by which the housing members are joined together is that the arrangement not detract from the appearance of the instrument and that it be readily usable by a serviceperson yet concealed so as not to encourage disassembly by the user. The latter is especially important where the telephone instrument is provided to the user on a lease basis rather than being sold.